Capital Gains on Sale of Rented House

My fiance and I both have a house each. We are getting married in January and are going to rent out my house and move into my girlfriends. We want to do this house up and the rent it out again and move back into my house. How will this work with my house when I go to sell with regards to Capital Gains tax? I know that CGT is not applicable on prinical primary residence's. Therefore how will CGT be treated on my PPR which I also rented out for a year during my ownership?

You calculate the CGT under normal rules.
Then you get exemptions:
Period you were living in the house
Last 12 months
The CGT is appotioned for the taxable period

Eg:
Taxable gain = €20,000
Period of ownership 20 years
Period living in 15 years
Last 12 months 1 year
Rented out for last 5 years

Taxable gain = €20,000 x 4/20 = €4,000
Less annual exemption €1,270 = 2,730 @ 22% = €600.60

Note that the rate of CGT is now 25% since April 7 2009.